1. Field of the Invention
The present invention relates to a liquid crystal display employing a black insertion driving method.
2. Description of the Related Art
The low response speed of conventional active matrix-type liquid crystal displays employing the hold driving method results in undesirable after-images or blurring when a moving picture is displayed. To improve the response speed, large liquid crystal displays for television receivers compare the image signal of a previous frame with the image signal of the present frame and provide an overdrive voltage that overlaps the image signal according to the comparison result. However, this procedure is inapplicable to small liquid crystal displays having a limited number of circuits and requiring low power consumption.
In order to solve the problems of the hold driving method for liquid crystal, an impulsive driving method has been suggested. The impulsive driving method includes black insertion driving in which a first image is displayed on the screen using normal image signals and then a second image is displayed using black image signals so that the normal image signals and the black image signals are alternately displayed on the screen.
According to another example of the impulsive driving method, a backlight is shut-off during a predetermined period corresponding to 40% of a frame period. However, if the backlight is shut off over the whole area of the screen, the upper screen and lower portions of the screen appear differently.
Although various techniques have been proposed to improve the response speed and the hold driving method of liquid crystal, such techniques are unsuitable for small-sized or middle-sized liquid crystal displays having a small number of circuits and requiring low power consumption. For example, since a large-sized liquid crystal television set uses many cold cathode fluorescent lamps (CCFL) or light emitting diodes (LEDs) as a backlight unit, the backlight scanning method is suitable. However, since the small-sized or middle-sized liquid crystal displays employs one or two CCFLs and one to three LEDs, the backlight scanning method is not as suitable.
In the black insertion driving method because image signals are written twice within one frame period the driving frequency becomes high, so that power consumption is increased. For this reason, the black insertion driving method is rarely employed in the small-sized or middle-sized liquid crystal display having a small number of circuits and requiring low power consumption.